地層下陷區地下水優選調配對淹水潛勢之影響分析

Abstract

本研究目的在探討地層下陷與淹水潛勢之關係，並據此建立地下水管理模式在滿足地下水需求量之前提下，求解最佳抽水量於時空之分配，達到降低地層下陷速率，間接地減緩因地層下陷而增加之淹水潛勢，以探討地下水優選調配對於淹水潛勢之影響。 本研究以雲林北排水系統為研究區域，首先利用地層下陷模式預測未來10年之累積下陷量，以推估10年後之地形；接著再利用SOBEK淹水模式分別模擬現況與10年後之渠道出水高與淹水深度，以探討地層下陷對淹水潛勢之影響。為了減緩地層下陷對未來淹水潛勢之影響，本研究發展了地下水管理模式，其可推求最佳之抽水時空分布以最大限度避免淹水潛勢因地層下陷而增加，且亦同時滿足地下水需求量。待管理模式建立後，本研究共研擬五個不同方案並推估其相應之最佳抽水量。應用結果顯示，各方案相較於無地下水管理時，地層下陷與淹水深度皆有改善效果，顯示對於地層下陷敏感區之淹水治理，亦應結合地下水管理之非工程措施，以達整體性地減緩地層下陷與減災防洪之目標。

In this study, the land subsidence and inundation models were utilized to numerically investigate the effects of pumping induced land subsidence on the freeboard and inundation depth. After realizing how the freeboard and inundation depth would be varied due to long-term land subsidence, a groundwater management model was developed to mitigate the effect of land subsidence on flood hazard. The management model determines the proper pumping strategy such that the goals including (1) controlling land subsidence; (2) preventing the flood hazard to be deteriorated in the future; and (3) satisfying the groundwater demand can be optimally achieved. The study area is northern Yunlin drainage system. To investigate the effects of land subsidence on flood hazard, firstly, the spatial distribution of accumulative land subsidence between 2012 and 2021 was predicted by a process-based land subsidence model. The digital elevation model (DEM) and channel geometry in 2021 were produced based on the predicted land subsidence field along with the present topography data. Then, the freeboard and inundation depth before and after ten years land subsidence were simulated by the SOBEK Suite. To mitigate the effect of pumping induced land subsidence on flood hazard, a groundwater quantity management model was developed. The management model determines the optimal pumping patterns which prevent the flood hazard to be increased due to long-term subsidence while satisfy the groundwater demand. Five scenarios were considered and the corresponding optimal pumping patterns for the study area were obtained by the developed management model. The results show that groundwater management can efficiently prevents the flood hazard to be deteriorated. Therefore, in addition to traditional structure measure, groundwater management should also be incorporated into flood regulation project for land subsidence prone area.